Continuous freeze dryer

ABSTRACT

Arrangement for continuously and automatically lyophilizing material comprising freezing the material, pulverizing the frozen material, circulating the material along a screw conveyor while exhausting the ambient gas to heat the material and expose particles of material to heat, regulating the heat supplied by reversible refrigeration, alternately exhausting said ambient gas in first and second cold traps, sequentially finishing partially treated material in at least first and second finishing zones and discharging the material into containers without breaking the vacuum.

United StatES Patent 1 Gottfried 1 3,731,392 [45 May 8,1973

[54] CONTINUOUS FREEZE DRYER [76] Inventor: Herbert Gottfried, 3441 5thSt., Ocean Side Long Island, N.Y.

[22] Filed: Feb. 25, 1971 [21] Appl. No.: 118,934

[52] U.S. Cl ..34/5, 34/92 [51] ..F26b 5/06 [58] Field of Search ..34/5,192

[56] References Cited UNITED STATES PATENTS 3,445,247 5/1969 Baerwald..34/92 X 3,477,137 11/1969 Gelder; 34/92 X 3,300,868 l/1967 Anderwert....34/92 X 3,271,874 9/1966 Oppenheimer ....34/92 X 3,352,024 11/1967Mellor ....34/92 X 3,314,160 4/1967 Forkner ..34/92 3,088,222 5/1963Mace et al ..34/92 FOREIGN PATENTS OR APPLICATIONS 1,048,830 1/1959Germany ..34/92 Primary ExaminerWilliam F. ODea AssistantExaminer-William C. Anderson Attorney-George B. Oujevolk [57] ABSTRACTArrangement for continuously and automatically lyophilizing materialcomprising freezing the material, pulverizing the frozen material,circulating the materi a1 along a screw conveyor while exhausting theambient gas to heat the material and expose particles of material toheat, regulating the heat supplied by reversible. refrigeration,alternately exhausting said ambient gas in first and second cold traps,sequentially finishing partially treated material in at least first andsecond finishing zones and discharging the material into containerswithout breaking the vacuum.

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CONTINUOUS FREEZE DRYER BACKGROUND OF THE INVENTION The presentinvention relates to a system for drying substances which deterioratewhen subjected to elevated temperatures; and more specifically, itconcerns the process called freeze-drying, i.e., lyophilization.

BRIEF DESCRIPTION OF THE ART OF FREEZE DRYING In a freeze dryingprocess, material to be dried is subjected to a low temperature so thatthe water present in the material goes over to the solid state formingice crystals. Ice, even though at low temperatures, has a substantialvapor pressure. If the pressure above the ice is lowered below thisvapor pressure, then the ice will evaporate.

Freeze drying, as generally practiced, is a batch process. The frozenmaterial is placed in pans or other containers, in a vacuum chamberwhere freeze drying proceeds. After evaporation of the water, thematerial is removed from the vacuum chamber for further processing. Thisis a slow process requiring a long period of time for complete drying.For example, fruit juices such as orange and lemon juice require severaldays to produce substantial amounts of dried material. In these cases,the residue, if not completely dry, is hygroscopic and will readily pickup moisture.

Material which is not completely dry will not age well, spoilageoccurring even when kept in the refrigerator. It is essential that thewater be removed so that the vapor pressure above the material is of theorder of 25 microns or less at ambient temperatures before the materialcan be considered completely dry. Thus with present instrumentation,while one may fairly rapidly evaporate 80-90 percent of the waterpresent, the last -20 percent takes long periods of time. Further,present instruments do not permit ready automation of the system.

OBJECTS OF THE INVENTION It is therefore an object of this invention toprovide an instrument for continuous freeze drying which starts from theraw material such as foods (e.g., fruit juices, meats, vegetables), andbiological materials, which are heat sensitive, and automatically andcontinuously prepare a dried material, stable for extended periods oftime.

Another object of the present invention is to provide an instrument fordehydrating materials more rapidly than by present day conventionalprocesses, without lessening the quality or stability of the finishedproduct.

Still another object of the present invention is to provide aninstrument for-preparing a product with an extremely low water contentso that the material, in most cases, can be stored at ambienttemperatures in sealed containers.

Yet another object of the present invention is to provide an instrumentfor preparing freeze dried materials without attendance being requiredby an operator, except to supervise the loading and unloading of theinstrument.

REQUIREMENTS OF A FREEZE DRYING SYSTEM A freeze-drying system thereforerequires:

A. A means for cooling the material to the frozen state.

B. A means for creating a vacuum, usually a vacuum pump.

An additional requirement is that the water evaporated does not enterthe vacuum pump in substantial quantities so as to condense there. Forthis reason a cold trap at a lower temperature than that to which thematerial to be dried has been cooled, is needed. This requires a thirdcomponent for the system, namely,

C. A cold trap.

In addition, as freeze drying proceeds it is required to supply heat tothe material to be dried, at a controlled rate, so that the heat ofevaporation is supplied, but the freezing point is not exceeded. Thisusually comprises exposing the outside of the container, where thematerial being dried is located, to a ambient temperature. In somecases, heated coils or infra-red rays are employed to supply this heat.A fourth component is then required.

D. Means for supplying heat to the material being freeze dried withoutraising the temperature above freezing.

SUMMARY OF THE INVENTION Generally speaking, the object of the inventionis to provide means for exposing, continuously, each and every particleof triturated frozen material to a source of controlled heat, in avacuum, so that all moisture in the material can be removed, and toperform this function in a completely automatic manner. Thus, in theapparatus herein contemplated, material to be processed is first frozenand ground. It is then introduced under vacuum to a treating chamber.Within this treating chamber are agitating means, e.g., screw conveyormeans for moving the material longitudinally across said chamber to oneend thereof, during this process exposing all particles of the materialto the blades of said conveyor and walls of the container. A return pathfor the material is provided to guide the material back from the one endto the other end of the chamber. Reversible refrigeration means areprovided to cool or heat the chamber walls so as to maintain thetemperature within a predetermined range. A vacuum pump and cold traparrangement constantly evacuates gas formed by moisture in the chamberand, vacuum discharge 'means are provided to discharge the treatedmaterial from the chambers into packing containers.

The invention, as well as other objects and advantages thereof willbecome more apparent from the following detailed description when takentogether with the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a type of block diagramrepresentation of the inventive concept when viewed along line 1 l ofFIG. 2, which cuts across the principal components of the instrumentherein described;

FIG. 2 shows a partly schematic, partly perspective explanation of theinstrument contemplated herein with parts broken away and in section todescribe the operation of the components; 7

FIG. 2a illustrates the principles of a reversible refrigeratorarrangement which is useful herein;

FIG. 3 presents a modification of the inventive concept described inFIG. 2 in a view somewhat similar to DETAILED DESCRIPTION THE OVERALLAPPARATUS According to the present inventive concept as illustrated inFIG. 1, raw material to be processed in the apparatus 10, such as citrusjuices, meats, vegetables or biological materials are first introducedinto an input zone 12 where the material is maintained at a constantlevel. From the input zone 12, the raw material is cooled in a pipe 14and goes to a freezing zone 16. In the freezing zone 16, the rawmaterial is caused to travel across an elongated chamber by a screwconveyor. The travel path is surrounded by cooling coils and the screwconveyor terminates in a crushing area having specially madeconvolutions to crush and pulverize the raw material. The raw materialis then transferred to a lyophilization zone 18 across a valve. In thislyophilization zone, the raw material is kept in constant movement whilethe zone is exhausted of moisture by means of a vacuum pump. This zonemay consist of one or two chambers. If a two stage arrangement 20, 20ais used, as shown in FIG. 1, about 50 percent of the moisture is removedin the first chamber while up to 90 percent of the moisture is removedin the second chamber. The lyophilization zone 18 is surrounded by thecoils 22 of a reversible refrigerator. l-Ieretofore, one of the problemsin connection with freeze drying was the fact that only the outer layerof material was treated whereas the moisture in the middle of a lump ofmaterial was insulated from the heat source so that the moisture wasretained. However, according to the present inventive concept thematerial is constantly moved, turned and agitated so that lumps are notformed and each and every particle of material is acted on by theheating coils 22 and the vacuum suction means. Generally, the materialwill remain in the two chambers of the lyophilization zone for upwardsof several hours. During this time, about ninety percent of the moisturewill be removed. The treated material is then transferred sequentiallyto one of three chambers of the finishing zone 24, 26, 28, across motoroperated valves 30, 32, 34. The chambers in this finishing zone aresimilar to those in the lyophilization zone and also cooled or heated byreversible refrigerator coils. How ever, in the primary chamber 24 ofthe second zone the input material is already 90 percent moisture free.After the first batch of material from the lyophilization zone entersthe primary chamber 24, the lyophilization zone 18 will have an emptychamber which is then refilled'with material from the freezing zone 16so that the two chambers of the lyophilization zone 18 remain inoperation, as well as the primary chamber of the finishing zone. Whenthe lyophilization zone 18 has again removed about 90 percent of themoisture in the second chamber thereof, the material is againtransferred, but this time across valve 32 to the secondary chamber 26of the finishing zone. At this time, both primary chamber 24 andsecondary chamber 26 are processing material. The two chambers of thelyophilization zone 18 are again kept filled, and again 90 percent ofthe moisture is removed from the material and this time the treatedmaterial is sent across valve 34 into last chamber 28. Thus, after awhile, the two chambers of the lyophilization zone-18, as well as thethree chambers of the finishing zone are processing material, theprocessing time in the lyophilization zone being about one-third thetime required for the processing'in any of the three chambers 24, 26, 28of the finishing zone.

After the material in chamber 24 is completely dried, the temperaturewill tend to rise. When it reaches ambient temperature, the signal light36 from chamber 24 will light up. This will act on photocell 36a causinga container 38 to stop under valve 24b. When the secondary chamber 26 isready, light 40 of the secondary chamber will light up to act onphotocell 40a. This will cause the next container to stop under valve26b of secondary chamber 26. The same thing takes place with the lastchamber and the process is then repeated.

It will be noted that at,all times a finishing chamber remains ready toaccept the load from the lyophilization zone. Thus, the total process iscontinuous and automatic. I

In the description of the invention which follows, three differentembodiments are described in connection with the lyophilization andconstant movement zones. For ease of presentation, the most complicatedembodiment is described first. However, the other embodiments areequally important and indeed, the simplest embodiment is in many casesmore advantageous, since it has less moving parts and consequently, isless apt to require repairs.

THE INPUT ZONE AND FREEZING AND CRUSI-IING ZONE The input zone 12 is fedby a spigot 42 into a liquid container 44 maintained at a constantlevel. This is accomplished by first and second electrode 46, one ofwhich is located within and the other without the liquid. One electrodeis tied to the grid and the other to the cathode of a vacuum tube 48.Thus, if the liquid level does not touch the grid electrode, currentflows from the cathode to the plate. When the liquid slurry level issuch as to touch the grid electrode, grid current flows, a relay isenabled and the liquid level is shut off. Liquid slurry in container 44drops along pipe 50 to a work unit. Pipe 50 is surrounded by coolingcoils 52 designed to keep the slurry cool, the coils being at about 0 toabout 5C; This work unit is the freezing zone 16 and consists of anelongated cylindrical chamber 54, disposed at about a 30 inclinationfrom the vertical, also surrounded by cooling coils 56. The temperatureof these cooling coils is about 40C. This causes the material to freezeto a solid state. In the center of cylindrical chamber 54 is a screwconveyor 58 disposed at an angle to thevertical. Thus, pipe 50 conveysthe raw material to the top of the chamber. In the screw conveyor 58,the last few upper convolutions 60 have a special cutting configurationto crush the icy material.

The material moving along screw conveyor 58 is to be transferred to thelyophilization zone 18. However, after the transfer, while the materialis being processed in the lyophilization zone 18, the screw conveyor 58of the freezing zone 16 does not stop turning. Indeed, if it were tostop, the material on the screw conveyor 58 would lump together and jamthe conveyor. Thus, when not transferring material across valve 20, thescrew conveyor turns slowly at an idle speed of about 1 rpm. to keep thematerial from freezing solid. In this state, the contents merely slidearound and does not advance.

From the foregoing, it can be seen that the liquid to be frozen andlyophilized arrives from a storage chamber through a spigot 44. Theopening of the spigot is controlled by a solenoid valve so that aconstant level is maintained in one leg of what comprises a V tube. Oneleg of the V tube is a pipe leading from the constant leveling device tothe second leg of the tube which comprises a combination driving screwconveyor and crushing heads, formed in several of the outer convolutionsof the screw conveyor.

The constant level is maintained by two platinum wires, one of whichdips into the liquid and is grounded and attached to the cathode of anelectronic tube. The

second wire is set at the level desired. This second wire is attached tothe grid of the electronic tube. The electronic tube acts as anelectronic switch to close a relay when the level of the liquid reachesthe second wire, closing the circuit. A transistor circuit can be usedin a similar fashion. 7

The closing of the relay activates the solenoid valve so that the liquidstops flowing into the V tube. This valve then opens when the liquidlevel drops. In this way a constant level is maintained.

The liquid travels down the V tube until it reaches the leg of the Vwhere the start of the screwconveyor is located. This screw conveyor isdriven by a motor arrangement 62. It serves to lift the liquid while itis being cooled by the cooling coils.

As the liquid first descends and then ascends the V, it is cooled andeventually freezes. The stainless steel lifting screw conveyor serves tobreak up the ice into chunks as it is formed. These chunks are liftedinto the grinding and flaking area. In this area, the convolutions ofthe screw take on the form of sharp pointed wedges or cutting blades.These flake and grind the ice so that when it reaches the exit zone ofthe V tube the material is in the form of a coarse ground powder.

FIRST LYOPHILIZATION ZONE Thus, lyophilization zone 18 comprises anelongated cylindrical chamber 66 also inclined from the vertical atabout 30 and held in this chamber 66 is a cylindrical partition 68 whichis fastened to the chamber wall by spokes 69. Within the cylindricalpartition 68 is a central screw conveyor 70. Central screw conveyor 70has a central shaft 72. The material treated travels up the centralscrew conveyor and over the cylindrical partition 68. Disposed aroundthe cylindrical partition 68 is an outer screw conveyor 74 which willpush the material downwards along the partition wall. This outer screwconveyor 74 does not extend fully along the entire length of thechamber. There are at most one or two convolutions. The centralpartition 68 does not extend the full length of the chamber so that thewall does not prevent the first and second outer convolutions of theouter screw spiral 74 from passing from the central shaft 72 over thewall. The outer screw conveyor 74 extends only partly along the outerwall since it is only connected to the central shaft at one extremity.As the chamber 66 is substantially vertical, material must be pushedupwards by the inner screw conveyor 70 until past the partition wall.The material will tumble in the space between the partition outer sideand the chamber inner wall and will travel back downwards to the bottomof the chamber along the partition wall.

In addition to the continuous movement just described by the screwconveyor arrangement, the first and second chambers of thelyophilization zone have two other features namely: a reversiblerefrigeration arrangement, and, a vacuum pump cold trap arrangement.Both of these will be described in greater detail herein.

Thus, as material is transferred from the freezing and crushing zone 16to the first lyophilization zone 18 across valve 62a, a vacuum pumparrangement is started so as to form a vacuum in first chamber 66. Atthis time the chamber 66 is sealed.

When the crushed ice reaches the first lyophilizing zone 18, it is onlya few degrees below the freezing point. The application of the vacuumcauses first a rapid evaporation process to proceed. This cools the icefurther to temperatures below lOC. The ice becomes harder as traces ofliquid are frozen. During this process, the rate of evaporation of theice is so rapid as to cool the ice rapidly. Contact with the rotatingdouble screw conveyor supplies the heat required for the heat ofvaporization.

' As the screw conveyor rotates in the chamber, the mechanical energy isconverted to heat. It is well known that mechanical energy generatesheat. Thus, the rate at which heat is supplied is determined by the rateat which the rotor rotates. In addition cooling coils add or subtractheat and thus maintain a constant temperature at a constant speed ofrotation.

When a balance has been reached between the cooling process due toevaporation, and the heating process due to rotation, so thatevaporation is taking place without melting of the ice, and with thetemperature remaining constant, the lyophilizing conditions or processconditions have then been established.

A motor 76 drives the screw conveyor in the vacuum chamber. This motor76 is connected to the shaft of the rotor which extends out of thechamber through a vacuum seal similar to the one described in US. Pat.

Nos. 2,419,074 and No. 2,454,340, or some other similar vacuum seal.

After permitting the lyophilization process to be established at ambientroom temperature, the temperature is slowly raised in the lyophilizationchamber by means of the coils from the reversible refrigeration means,so that the wall temperature reaches 30 to 70C, depending upon thelyophilization rate and stability of the material. It must be pointedout that while the wall temperature is above room temperature, thetemperature of the material remains well below freezing because of therapid evaporation process.

Treatment in the chamber continues until the gas pressure in the chamberreaches 200 microns or less at 50C. This usually takes approximately twohours, the exact time depending on the material, the capacity of thechamber, the operation of the vacuum pump'and cold trap subsequentlydescribed herein.

Thus, in the lyophilization chamber 66, the material is circulatedforward, up, back down, and forward again. In addition, the material isbeing lifted and circulated against the walls of the chamber in a spiralfashion. This results in intimate contact of the particles of materialwith the screw conveyor and container walls permitting efficient accessof the heat to the material to be lyophilized. This solves a majorproblem with present systems.

It is to be noted that the problem of getting heat to each particle issolved in this invention by bringing the heat to each particle by themechanical motion of a mixing and circulating device. This produces areadily controlled temperature at the surface of each particle.

In the present invention, a central rod supports a first screw conveyorand, attached to the first screw conveyor is a second screw conveyor sothat both move together. Rigidly attached to the wall of the containeris a stainless steel cylindrical partition containing the first screwconveyor, while the second screw conveyor, which does not completelyextend across the entire chamber, and indeed, may have only one or twoconvolutions, goes around the cylindrical partition. The inner screwconveyor drives the material forward and, when it reaches the end of itstravel, it piles up and is soon picked up. by the outer screw conveyorwhich moves it in the opposite direction. In this way, the materialcirculates from front to back. Since the outer and inner screw conveyorsalso lift material on each rotation, the material describes a spiralmotion forward and the material comes repeatedly in contact with thescrew blades and the walls of the container.

The center stainless steel separation may also be omitted. In this casethe inner and outer screw conveyors, running counter to each other, areboth con tinuous and rigidly attached. In this case the material pushedby the outer spiral packs and forms a wall so that the material beingpushed in the inner spiral moves counter to this wall of material.

While the ball valve 62 is closed, operation of the screw conveyor inthe freezing zone 16 is in an idling position, rotating only slowly at lr.p.m., or less to prevent impaction of the ice, but not fast enough tolift it. At the same time no new liquid is coming in because the spigot22 is closed. This permits the lyophilization chamber to causecirculation of the material until a vacuum of less than 200 microns isreached. This low pressure starts a timer switch. Lyophilization andcirculation is continued for about an additional 1 hour. At this pointvalve 78 opens.

Communication then exists between the first and second lyophilizationchambers 66 and 66a. The second lyophilization chamber is at less than100 microns, so that the vacuum is not broken. All the material in thefirst lyophilization chamber 66 now empties into the secondlyophilization chamber 66a. This chamber is almost identical to thefirst chamber and'need not be described in detail. In fact, for someapplications this second chamber of the lyophilization may be omitted.

After about 50 percent of the moisture has been removed in the firstchamber, the material is transferred to the second chamber kept under ahigher vacuum. Here, the process proceeds as in the first chamber,except that upwards of 90 percent of the moisture is then removed.

Up to this point, two features of the first lyophilization and constantmovement zone have not as yet been described. These features are thereversible refrigeration, and the vacuum pump and cold trap.

THE COLD TRAP AND VACUUM PUMP ARRANGEMENT The cold trap and vacuum pumparrangement 80 is connected to the chamber 66 of the first zone by anexhaust pipe 82. Pipe 82 splits with first and second branches each witha valve 84, 84a. Each branch has a cold trap 86, 86a surrounded byreversible refrigeration coils 88, 88a. Each cold trap 86, 86a is inturn connected to a central pump 90 across valves 92, 92a. Valves 92,92a operate together with valves 84, 84a. Thus, in effect, there is anexhaust line from the chamber 66 to the vacuum pump 90 alternatelyacross cold trap 86 and 86a. The cold trap is nothing more than-a hollowvessel with input and exhaust openings at the top of the vessel,surrounded by reversible refrigeration coils 88, 88a, and drains withvalves 94, 94a.

During operation, the vacuum pump continues to operate uninterrupted. Atfirst valve 924 and valve 84a are closed. Valves 92 and 84 are open.Condensation of ice takes place in cold trap 86. Cold trap 86 is of suchmagnitude that it can take all of the condensate from one charge of thelyophilizing chamber. When the lyophilizing chamber 66 begins to unload,ball valves 92 and 84 close. Drain valve 94 opens. Cooling coils aroundcold trap 86 now become heating coils due to reversal of the action ofthe reversible refrigeration. The ice begins to melt and the water goesdown a drain across drain valve 94. In the meantime, valves 92a and 840are opened, and drain valve 940 has closed. The coils around the secondcold trap 86a become cooling coils. Lyophilization of the next charge inthe lyophilizing chamber results in condensation in the second cold trap860. When this trap is full the cycle is repeated, the first cold trap86 becoming cold, while the second cold trap 86a is defrosted.

THE REVERSIBLE REFRIGERATING ARRANGEMENT A reversible refrigerating unit96 has two sets of coils 98, 100 separated by a narrow orifice 102 witha pump 104 to compress the gas contained in the system. As the gas iscompressed in coil 100 preceding the narrow orifice 102, its temperatureis elevated. As the gas expands into a second coil 98 on the other sideof the orifice 102, it cools. Thus, there is a cool set of coils 98 anda hot set of coils 100, and a pump 104 maintaining the differential inpressure.

The hot set of coils 100 is cooled by outside means (air or water),shown as a fan 1%, and thus, the cold set of coils gets colder in eachpass so that soon it can be used for freezing materials.

Now the pump may be reversed. In which case, the function of the twosets of coils is reversed. The hot set of coils now becomes the cold andthe cold set of coils becomes hot. Normally, a fan 106, 1060 serves tocool the hot coils. When the inlets and outlets of the compressor arereversed, the coils around the container contain the gas under pressure.These then become the hot coils. By alternately reversing the compressordirection, a constant temperature can be readily maintained in a chamberfrom -80C to +75C, that is from very cold to hot. This is the rangewhich is used in the various chambers of the present invention. Toenhance the heating and cooling, coils can be passed through the screwconveyor.

OPERATION OF THE LYOPHILIZATION PROCESS Thus, to briefly review theoperation of the apparatus hereinbefore described, it can be stated thatmaterial to be lyophilized needs first to be frozen and then pulverized.This is done in the freezing and crushing zone 16. Two general methodsmay be used. The preferred procedure is to cool the material to thesolid state by refrigeration and pulverize it. As the material travelsalong a screw conveyor, an alternative procedure is to drop thematerial, one drop at a time, or particle by particle into liquidnitrogen. The frozen pellets so formed are then pulverized.

The material is transferred by means of the screw conveyor to alyophilizing zone 18 of constant move ment. Here the material is subjectto high vacuum. A reversible refrigeration unit herein described,maintains the wall temperature at 25 to 75C. This requires heat and thereversible refrigeration supplies this heat by being operated in areverse manner. The reason for this is that the lyophilization processremoves the heat of vaporization from the material. While thetemperature on the walls of the container is above ambient temperature,the temperature of the ice crystals in the container is at -20C, orless. An electric heating coil is not satisfactory at this stage sincein the event that the temperature becomes too high, the reversiblerefrigeration needs to be reversed to cool the chamber 66. Thus, acooling and heating system is needed at the lyophilization stage. Theagitation and movement of the material also generates heat and this isthe main source of heat utilized in the process. This also may supplyexcessive heat under certain circumstances and then the reversiblerefrigerator needs to act as a coolant.

The lyophilizing zone 18 communicates with a vacuum pump to create thevacuum. interposed between the vacuum pump and the lyophilizing zone isa condensing zone consisting of two cold traps used alternately wherethe evaporated water is condensed.

iii

Here the temperature is maintained at from -40C to -C in order toascertain that the vapor pressure of the ice in the condensing zone islower than that in the lyophilizing and constant movement zone.

It is apparent that after a period of operation, the cold trap in thecondensing zone will become full of ice and require defrosting. For thisreason the condensing zone consists of two cold traps, each connectingto the pump and to the lyophilizing zone, through ball valves and eachsupplied with a separate reversible refrigerator unit.

The first cold trap is defrosted by the reversible refrigeration raisingthe temperature to above freezing to melt the ice therein. A drain,supplied in the cold trap, opens and the water runs down the drain. Whenall the water has drained out, the drain valve closes and therefrigerator reverses to cool the cold trap to -40C to -80C. The firstcold trap is now ready to accept a second load of ice after the secondcold trap has become full. The process is then repeated with the secondcold trap. In this manner, in a continuous automatic fashion thecondensate is frozen and removed.

During the initial operation, the chamber being loaded is at ambientpressure, while the other chambers in the system are separated from thischamber by ball valves, vacuum being maintained in these other chambers.When the first chamber has been fully loaded with ice, it is sealed offfrom the atmosphere and evacuated. Loading from one chamber to the nextdoes not break the vacuum in this manner, when ball valves between thechambers are opened.

The lyophilization zone 18 is preferably a complex of two or moresimilar chambers 66, 66a. In the first chamber, vacuum is applied untila pressure of less than 200 microns is reached. This signifies thatlyophilization is in progress. Establishment of lyophilization meansthat the rate of evaporation is sufiicient to maintain the material in afrozen state, without outside cooling. This also means that the ice isusually at least 10C below the freezing point and is frozen hard. Thefunction then of the first chamber is to establish firmly the conditionsof lyophilization.

The material is now transferred to the second chamber where the vacuumis maintained at below 100 microns until approximately percent of themoisture has been removed. Thus, after treatment in the firstlyophilization chamber 66, and after aboui. 50 percent of the moisturehas been removed, ball. valve 78 which is also motor driven, opens andthe material in chamber 66 is transferred to chamber 66a. Valve 78 thencloses and valve opens admitting air and the material from the grindingand flaking area into the first lyophilizating chamber. Valve M closes,the vacuum pump is activated, and motor 62 goes to idling speed. Thecycle for the first lyophilizating chamber is now repeated.

The second lyophilizating chamber is constructed in a manner similar tothe first lyophilizating chamber. The volume of the powder is markedlyreduced in the first lyophilizating chamber since approximatelytwothirds of the water has been removed. For this reason, the secondiyophilization chamber may be smaller for many applications. As analternative, if of the same size, the second lyophilization chamber maytake several successive loads from the first lyophilization chamber.

In the second lyophilization chamber, lyophilization continues until thepressure is brought down to less than 75 microns at temperatures'rangingfrom 30 to 70C, depending upon the stability of the material.

Second lyophilization chamber 66a communicates with three finishingchambers. These are called finishing chambers because it is in this areathat the material is finally dried and ground before being packaged. Thestructure of the finishing chambers is similar to first and secondlyophilizating chambers.

THE FINISHING ZONE When the material in the second lyophilizatingchamber of the lyophilization zone has reached a vapor pressure of lessthan 75 microns at 30 to 70C it usually indicates that its moisturecontent has been lowered to less than percent. More time is required toremove the last traces of moisture than is required to reduce themoisture content in the first two lyophilization chambers. The contentsof the second lyophilization chamber are therefore transferred to afinishing primary chamber 24 under vacuum. As described before, chamber24 is one of three finishing chambers. When the product in the secondlyophilization chamber is again ready for transfer, this is thentransferred .to the finishing secondary chamber 26. When a third chargeis ready from the second lyophilization chamber 66b, this is transferredto last finishing chamber 28. The finishing chambers are maintained attemperatures ranging from 4 to 40C. The reason for using the lowertemperatures is because of the fact that as the material dries, itstemperature rises to wall temperatures. For certain biological products,chambers 24, 26, 28 are maintained below 10C. For fruit juices thetemperature may be elevated to 40C. In any case the wall temperature ofchambers 24, 26 and 28 are lower than that of the chambers in the firstzone where ice is present at all times.

The outer screw conveyors of the finishing chambers have a few turnswhich are wedge-shaped so as to pulverize the product, since some driedpowders obtained from materials such as orange juice, tend to cake andform a compact mass as they approach dryness. This prevents the completedrying of the material within the cake. For this reason the materialneeds to be powdered. I

After loading of finishing primary chamber 24, chamber 66a receives acharge from chamber 66 and chamber 66' is loaded from chamber 54. Duringthis process the last chamber 28, is unloaded. In this case a ball valveopens and the contents of chamber 28 are emptied into an evacuatedplastic coated metal container on an endless belt arrangement.

The treating time in the finishing chambers is much longer than in thelyophilization chambers. Indeed, treatment in the lyophilization zonemay be about 4 hours and 12 hours in the finishing chambers. The onlysignificant difference between the finishing chambers 24, 26, 28 andlyophilization chamber 66 is that they have a vacuum dischargearrangement.

PACKAGING ZONE After the material in chambers 24, 26, 28 aresuccessivelyfreeze dried, the contents of these chambers must be transferred toappropriate containers. Two

proceedures may be followed. The packaging zone may be kept under aninert gas, such as nitrogen. Or, the empty containers may first beplaced in a tray lyophilization apparatus as described in the Natelsonand H. Gottfried et a]. U.S. Pat. No. 3,293,772, and then sequentiallyreleased and moved out under vacuum conditions on an endless belt. Thus,as the container enters the packaging zone, it either is undersubstantial vacuum conditions, or under inert gas ambient conditions.

The discharge of the product into containers 38 is done in packagingzone 110. Here, the containers 38, 38a will leave the entrance chamberand go along a belt and roller conveyor 39. Each chamber 24, 26, 28 inthe finishing zone has a light 36, 40, and 29 and a correspondingphotocell 36a, 40a, and 29a. Below each chamber is a lift for the beltand roller conveyor consisting of pairs of rollers 24a, 24b; 26a, 26b;28a, 28b. These roller pairs are held by a pivot and arm. As eachphotocell is enabled, it operates a solenoid pulling down two arms underthe chamber, thus lifting the roller pairs under the chamber. Thearriving container 38a hits a switch as it comes into position whichstops the belt and roller conveyor drive long enough to fill thecontainers and opens a valve 24V, 26V, 28V at the same time. As thecontainer lifts, it meets a flare on the mouth of the exit of thefinishing chamber. This flare on the mouth is covered with a rubber mat.Thus a close fit, mouth to mouth,-is made. As the exit valve of thefinishing chamber opens, a vacuum forms in the container due to thevacuum in the finishing chamber. This causes the container to adhere, asin the Natelson and H. Gottfried et al. U.S. Pat. No. 3,293,772. Thevacuum pump continues to operate, avacuum then forms in the container.The container is filled by the motion of the screw in driving the powderforward. When the container is full, the exit valve closes. The bleedervalve opens and the platform under the container is lowered. This causesthe container to fall away.

This portion of the instrument operates somewhat as described in theaforesaid U.S. Pat. No. 3,293,772, except that in the present case thecontainers move to the discharge orifice, whereas in the aforesaid U.S.Pat. No. 3,293,772, the material treated is stationary. During thefilling of the containers the suction pump arrangement of the finishingchamber keeps operating to remove any moisture in the containers.However, it is important to maintain .either a partial vacuum or aninert atmosphere in the packaging zone to avoid contamination of theproduct. Attention is directed to the fact that the lifting height ofthe containers to the discharge orifice of the finishing chambers hasbeen greatly exaggerated in the drawing to explain the operation. Inpractice, the roller pairs merely lift the belt a fraction of an inchand, there is no chance of the containers tipping over because of a highlift. a

Another example of a packaging zone is shown in FIG. 6 where thefinishing chambers are shown as chambers 124, 126, 128. Each finishingchamber is connected to a cold trap and vacuum pump arrangement 180,similar to the corresponding arrangement 80, herein before described.Each cold trap and vacuum pump arrangement has two cold traps 186,

186a, but each cold trap has its own pump 190, 190a, and each pump hasits own motor 191, 191a. Each cold trap has a reversible refrigerationunit 188, 1880, and each chamber 124, 126, 128, likewise has its ownreversible refrigeration unit 196. The chambers 124, 126, 128 operateexactly as described, with reference to chambers 24, 26, 28. Eachchamber has an output valve 124b, 1261), 128b, which leads to a screwconveyor 139. The screw conveyor 139 is kept under vacuum by acondensing unit 140 operated by a pump l90b driven by a motor 191a. Thecontainers are filled in a vacuum chamber 142 connected to the output ofthe screw conveyor 139. The filling of the containers has already beendescribed in connection with FIG. 5.

PROGRAMMING AND COMPONENTS To somewhat condense the lengthly descriptionand to avoid describing matters known to those skilled in the art, theprogramming and certain components have not been described at length.The valves between the various chambers are all ball valves operated bya motor. This permits a perfect vacuum to be maintained since when theball valve is shut there is substantially no leakage. Since many of thecomponents operate at low temperatures, electric motors to operate thevalves have been found to be more satisfactory than relays and solenoidsin most cases. Also, not described in detail are program means. Therespective chambers are discharged when the gas pressure therein reachesa certain pressure level. Then pressure gages actuate the respectivemotors opening and closing the proper valves. Since this function iswell known in the arts, an extensive description of these program meanshave been omitted from the description. If necessary, the separatefunctions can be performed by hand.

OTHER EMBODIMENTS The treating chambers described and shown in FIG. 2all have an inner and outer screw conveyor separated by a cylindricalpartition. A simple version is shown in FIG. 3. Here, chamber 166 hasonly a single screw conveyor 170 and a returnchute 168. With chamber 166inclined at an angle of between 15 and 30 from the vertical, the goodsreaching the top of the chamber readily fall down the chute back to thebottom of the chamber. It is possible to have a single horizontalchamber 266 with an inner cylindrical partition 268 and only an innerscrew conveyor 270. The return path 274 is over the inner cylindricalpartition 268. FIG. 4a shows a different version of the horizontalchamber 366 having twin screw conveyors 370, 374 separated by apartition 368. The configuration of the partition wall 368 and the screwconvolution permits the cycling of the material being treated. Thearrows in the figure show the path of the material as it moves duringlyophilization.

It is to be observed therefore, that the present invention provides fora freeze drying instrument having input means to introduce a controlledamount of raw material to a, freezing zone 16 having a freezing chamber54 with constant agitating means, e.g., a screw conveyor 58 therein. Thematerial is then discharged into the first chamber 66 of alyophilization zone 18 where the treated material is continuouslycirculated by a screw conveyor arrangement. The screw conveyorarrangement may consist of two screw conveyors 70, 74, one an inner, theother an outer conveyor, separated by a cylinder 68, or just a singlechamber 266 with a single screw conveyor 270 and a cylinder separation168a defining a return path 274a. It may also consist of two parallelscrew conveyors 370 and 374 separated by a partition wall 368 or asingle substantially vertical chamber 166 with a single screw conveyor170 therein and a return chute 168. Material is treated in the firstchamber for several hours to remove about 50 percent of the moisture. Itis then transferred to a second chamber 66a similar to the first chamberwhere the treatment is continued until up to percent of the moisture isremoved. The material is then sequentially transferred to one of threefinishing chambers 24, 26, 28, similar to chambers 66, 166, 266, 366where the treatment is continued for upwards of ten hours to remove theremaining moisture. The finished product is then discharged intocontainers under vacuum conditions.

EXAMPLE A typical example, on a pilot plant scale, is described asfollows:

Freshly pressed orange juice is cooled and partially frozen. The liquidportion is forced through a stainless steel screen and the ice whichseparates is washed with small quantities of cold water. In this manner,40 to 50 percent of the water is removed. This is the orange juiceconcentrate.

The instrument described in FIG. 3 is utilized. All chamber sizes are 2feet long by 16 inch diameter for a volume capacity of 2.5 cubic feet orapproximately 28 quarts.

The concentrate is placed in a storage vat cooled to 4C whichcommunicates with the solenoid valve and spigot of the instrument. Whenthe instrument is turned on the solenoid valve opens and the orangejuice is added to the V tube. There it is frozen and ground.

Twelve quarts of frozen and ground material are added to the firstlyophilization chamber which is cooled to 20C. The motor turns the screwassembly at 20 r.p.m. during the loading cycle. The ball valve closesand the vacuum is applied. For the next twenty minutes the outer wall iscooled to 20C while the screw rotates slowly (20 r.p.m.) until a vacuumof less than 300 microns is reached indicating that the lyophilizationprocess has been established. The, screw assembly now is rotated at 60r.p.m. As the pressure continues to fall, the wall temperature is slowlyincreased. When the pressure drops to 200 microns the wall temperatureis now raised to 70C with the reversible refrigerator coils.

The temperature is raised slowly so that no increase in pressure iscaused, the pressure remaining at less than 200 microns. If the presenceshould rise, the temperature is lowered rapidly .since it signifies aleak, and danger of melting of the material. The temperature is kept at70C, usually for approximately 3 hours. At this point, the temperatureis lowered to 50C and maintained there for approximately one-half hourwhen the pressure is now at microns or less. If maintained at 70C thepressure may rise indicating less water in the material and therefore,less evaporation and cooling per unit time.

When the total elapsed time is 4 hours, the contents of the firstlyophilization chamber are automatically transferred to the secondlyophilization chamber (maintained at 50C) by the action of the screwconveyor in driving the material forward. The screw assembly in thesecond lyophilization chamber also rotates at 60 r.p.m. The firstlyophilization chamber is now automatically reloaded with a second 12liters of frozen orange juice concentrate.

The second lyophilization chamber is maintained for four hours at 50C atwhich time the material is transferred to one of the three finishingchambers.

In the finishing chambers the wall temperature is programmed to besteadily reduced from 50 to C or ambient temperature. The reason forthis is that as the material dries, the rate of cooling decreases andno. cooling is occurring when the material is dry. The screw operates atr.p.m. in the finishing chambers. The material remains for 12 hours inthe finishing chamber. At the end of 12 hours, a timer activates thebelt drive which carries the empty glass or plastic coated metalcontainers. A light and photocell arrangement causes the glass containerto stop under the chamber ready for unloading. The container is filled'with the amount of powder equivalent to one quart of orange juice. Sincethe powder represents 12 liters of frozen orange juice concentrate or 24liters of orange juice, 24 containers are so filled.

The total elapsed time for this pilot plant is 20 hours (4 4 12) toproduce the first batch of lyophilized powder. Subsequent batches comeout at a rate of once every 4 hours. Subsequent batches are fed toalternate finishing chambers, the first finishing chamber beingre-utilized after emptying.

I claim:

1. The method of continuously and automatically lyophilizing materialcomprising the steps of:

a. freezing the material;

b. pulverizing the frozen material;

c. circulating the material from an inlet zone along a screw conveyorwhile exhausting the ambient gas to heat the material and exposingparticles of material to heat and recycling the material back to theinlet zone;

. regulating the heat supplied by the rate of rotation of thecirculating screw and by reversible refrigeration;

e. alternately exhausting said ambient gas in first and second coldtraps;

f. sequentially finishing partially treated material in at least firstand second finishing zones; and,

g. discharging the material into containers without breaking the vacuum.

2. In an automatic and continuous freeze drying instrument, incombination,

a. input means to introduce under vacuum a material to be processed inthe instrument;

. an elongated lyophilization chamber, connected to said input means,said chamber having screw conveyor means therein for conveying andagitating said material longitudinally in said chamber to one endthereof, including means for adjustably rotating said screw conveyormeans at predetermined speeds, said rotation also supplying heat to thechamber and means for controlling said adjustable rotating means forcontrolling the temperature in the chamber;

c. a return path coupled to said chamber for guiding material from saidone end to the other end of said chamber;

. reversible refrigeration means to cool or heat said chamber and thusmaintain the wall temperature within a predetermined range;

e. a vacuum pump and cold trap arrangement to constantly evacuate gasformed by moisture in said chamber; and,

f. vacuum discharge means to discharge treated material from the chamberwhile maintaining the vacuum in the chamber.

3. A device for the continuous dehydration of materials which aresensitive to heat which comprises,

a. a conveyor to continuously feed said material to be dehydrated to afirst freezing and crushing compartrnent;

. a reversible first refrigeration unit attached to said freezing andcrushing compartment; said freezing and crushing compartment havingmeans for pulverizing the frozen material, said first refrigeration unitsupplying a constant reduced temperature to said freezing compartment soas to freeze and maintain the material in a frozen state;

c. a lyophilizing and constant movement zone connected to said freezingand crushing compartment; said lyophilizing zone being attached to acondensing zone; said condensing zone being maintained at a lowtemperature by a second reversible refrigeration unit so as to condensethe moisture removed from the material being dehydrated;

. a vacuum pump attached to said condensing zone so as to maintain areduced pressure causing the -material in the lyophilizing zone to giveup its water and cool itself, thus remaining in a frozen state;

e. a third reversible refrigeration unit attached to said lyophilizingand constant movement zone so as to maintain a flow of heat to thematerial being dehydrated so as to supply energy required forlyophilizat'ion;

f. means for continuously agitating progressively advancing andrecycling the material in the lyophilizing and constant movement zone;and, a receiving and packaging zone attached to said lyophilizing andconstant movement zone so that the material can be removed from thelyophilizing and constant movement zone without breaking the vacuum inthe major portion of said zone in order for the material to be removedand packaged in a continuous mode;

h. and means for adjusting said continuously agitating means atpredetermined speeds, said continuously agitating means also supplyingheat to the lyophilizing and constant movement zone; and means forcontrolling said adjusting means for controlling the temperature in thelyophilizing and constant movement zone for controlling the temperaturein the zone.

. In a freeze drying instrument, in combination,

a. input means to introduce under vacuum a material to be processed inthe instrument;

b. an elongated lyophilization chamber, connected to said input means,said chamber having agitation conveyor means therein for conveying saidmaterial longitudinally in said chamber to one end thereof atpredetermined speeds, means for adjusting said agitation conveyor meansat predetermined speeds, said agitation exposing all parts of saidmaterial to treatment and heating said material, and means forcontrolling said adjusting means for controlling the temperature in thechamber,

. a return path coupled to said chamber for guiding material from saidone end to the other end of said chamber;

. refrigeration means to cool or heat said chamber and thus maintain thewall temperature within a predetermined range;

. a vacuum pump and cold trap arrangement to constantly evacuate gasformed by moisture in said chamber; and,

f. vacuum discharge means to discharge treated material from the chamberwhile maintaining a vacuum in said chamber.

5. An instrument as claimed in claim 4, wherein said refrigeration meansare reversible.

6. An instrument as claimed in claim 4, including a. in said inputmeans, constant leveling means and a cooled pipe (14) connected to afreezing zone 16); and,

said freezing zone comprising an elongated chamber having a screwconveyor therein and refrigeration means to heat and cool said freezingzone.

7. An instrument as claimed in claim 4, wherein said lyophilizationchamber is generally vertically inclined, said agitation means is acentral screw conveyor and said return path is a chute from the top ofsaid chamber to the bottom thereof on the outer side of said chamber,said material being carried upward by the screw conveyor and carrieddownwards by said chute.

8. An instrument as claimed in claim 4, wherein said lyophilizationchamber is substantially horizontal including first and second screwconveyors for conveying material in opposite directions, with apartition wall therebetween.

9. An instrument as claimed in claim 4, wherein said lyophilizationchamber is generally vertically inclined, said agitation means is acentral screw conveyor in said lyophilization chamber and said returnpath includes a cylindrical partition in said chamber.

10. An instrument as claimed in claim 9, including an outer screwconveyor with a few convolutions around said partition.

1 1. An instrument as claimed in claim 4, including at least first andsecond finishing chambers connected to said lyophilization chamber, saidfinishing chambers being constructed similar to said lyophilizationchambers and being coupled to said vacuum discharge means, the materialbeing first partially lyophilized in said lyophilization chamber untilambient pressure in said lyophilization chamber reaches a predeterminedlevel and then transferred to said finishing chamber when all remainingmoisture is removed.

12. An instrument as claimed in claim 10, including means forautomatically transferring material between chambers under vacuum.

1. The method of continuously and automatically lyophilizing materialcomprising the steps of: a. freezing the material; b. pulverizing thefrozen material; c. circulating the material from an inlet zone along ascrew conveyor while exhausting the ambient gas to heat the material andexposing particles of material to heat and recycling the material backto the inlet zone; d. regulating the heat supplied by the rate ofrotation of the circulating screw and by reversible refrigeration; e.alternately exhausting said ambient gas in first and second cold traps;f. sequentially finishing partially treated material in at least firstand second finishing zones; and, g. discharging the material intocontainers without breaking the vacuum.
 2. In an automatic andcontinuous freeze drying instrument, in combination, a. input means tointroduce under vacuum a material to be processed in the instrument; b.an elongated lyophilization chamber, connected to said input means, saidchamber having screw conveyor means therein for conveying and agitatingsaid material longitudinally in said chamber to one end thereof,including means for adjustably rotating said screw conveyor means atpredetermined speeds, said rotation also supplying heat to the chamberand means for controlling said adjustable rotating means for controllingthe temperature in the chamber; c. a return path coupled to said chamberfor guiding material from said one end to the other end of said chamber;d. reversible refrigeration means to cool or heat said chamber and thusmaintain the wall temperature within a predetermined range; e. a vacuumpump and cold trap arrangement to constantly evacuate gas formed bymoisture in said chamber; and, f. vacuum discharge means to dischargetreated material from the chamber while maintaining the vacuum in thechamber.
 3. A device for the continuous dehydration of materials whichare sensitive to heat which comprises, a. a conveyor to continuouslyfeed said material to be dehydrated to a first freezing and crushingcompartment; b. a reversible first refrigeration unit attached to saidfreezing and crushing compartment; said freezing and crushingcompartment having means for pulverizing the frozen material, said firstrefrigeration unit supplying a constant reduced temperature to saidfreezing compartment so as to freeze and maintain the material in afrozen statE; c. a lyophilizing and constant movement zone connected tosaid freezing and crushing compartment; said lyophilizing zone beingattached to a condensing zone; said condensing zone being maintained ata low temperature by a second reversible refrigeration unit so as tocondense the moisture removed from the material being dehydrated; d. avacuum pump attached to said condensing zone so as to maintain a reducedpressure causing the material in the lyophilizing zone to give up itswater and cool itself, thus remaining in a frozen state; e. a thirdreversible refrigeration unit attached to said lyophilizing and constantmovement zone so as to maintain a flow of heat to the material beingdehydrated so as to supply energy required for lyophilization; f. meansfor continuously agitating progressively advancing and recycling thematerial in the lyophilizing and constant movement zone; and, g. areceiving and packaging zone attached to said lyophilizing and constantmovement zone so that the material can be removed from the lyophilizingand constant movement zone without breaking the vacuum in the majorportion of said zone in order for the material to be removed andpackaged in a continuous mode; h. and means for adjusting saidcontinuously agitating means at predetermined speeds, said continuouslyagitating means also supplying heat to the lyophilizing and constantmovement zone; and means for controlling said adjusting means forcontrolling the temperature in the lyophilizing and constant movementzone for controlling the temperature in the zone.
 4. In a freeze dryinginstrument, in combination, a. input means to introduce under vacuum amaterial to be processed in the instrument; b. an elongatedlyophilization chamber, connected to said input means, said chamberhaving agitation conveyor means therein for conveying said materiallongitudinally in said chamber to one end thereof at predeterminedspeeds, means for adjusting said agitation conveyor means atpredetermined speeds, said agitation exposing all parts of said materialto treatment and heating said material, and means for controlling saidadjusting means for controlling the temperature in the chamber, c. areturn path coupled to said chamber for guiding material from said oneend to the other end of said chamber; d. refrigeration means to cool orheat said chamber and thus maintain the wall temperature within apredetermined range; e. a vacuum pump and cold trap arrangement toconstantly evacuate gas formed by moisture in said chamber; and, f.vacuum discharge means to discharge treated material from the chamberwhile maintaining a vacuum in said chamber.
 5. An instrument as claimedin claim 4, wherein said refrigeration means are reversible.
 6. Aninstrument as claimed in claim 4, including a. in said input means,constant leveling means and a cooled pipe (14) connected to a freezingzone (16); and, b. said freezing zone comprising an elongated chamberhaving a screw conveyor therein and refrigeration means to heat and coolsaid freezing zone.
 7. An instrument as claimed in claim 4, wherein saidlyophilization chamber is generally vertically inclined, said agitationmeans is a central screw conveyor and said return path is a chute fromthe top of said chamber to the bottom thereof on the outer side of saidchamber, said material being carried upward by the screw conveyor andcarried downwards by said chute.
 8. An instrument as claimed in claim 4,wherein said lyophilization chamber is substantially horizontalincluding first and second screw conveyors for conveying material inopposite directions, with a partition wall therebetween.
 9. Aninstrument as claimed in claim 4, wherein said lyophilization chamber isgenerally vertically inclined, said agitation means is a central screwconveyor in said lyophilization chamber and said return path includes acylindrical partition in said chamber.
 10. An instrument as claimed inclaim 9, includiNg an outer screw conveyor with a few convolutionsaround said partition.
 11. An instrument as claimed in claim 4,including at least first and second finishing chambers connected to saidlyophilization chamber, said finishing chambers being constructedsimilar to said lyophilization chambers and being coupled to said vacuumdischarge means, the material being first partially lyophilized in saidlyophilization chamber until ambient pressure in said lyophilizationchamber reaches a predetermined level and then transferred to saidfinishing chamber when all remaining moisture is removed.
 12. Aninstrument as claimed in claim 10, including means for automaticallytransferring material between chambers under vacuum.